1. Field of the Invention
This invention relates to a screw tightening machine in which a string of screws are fed from a magazine to a nose mounted on the forward part of the body of the machine and are driven out one by one from the nose.
2. Description of the Related Art
A magazine described in, for example, Japanese Patent Official Gazette No. Hei 1-60395 is known as an example for use in this type of screw tightening machine. This magazine is fixed to the body of a screw tightening machine and, inside of the magazine, a path along which a string of screws are guided is provided so that the screws are stably kept to smoothly carry out a screw tightening operation.
The screw tightening machine has a nose capable of, with respect to the body of the machine, moving in a direction in which a screw is tightened. In detail, the nose can protrude from or retract into the body of the machine. The screws kept in the magazine are fed to the nose. The nose to which the screws are fed moves relatively with respect to the body of the machine during the screw tightening operation, whereas the magazine from which the screws are fed is unmovably fixed to the body.
Accordingly, the screws 23 in the magazine 22 are pulled out of the magazine 22 when the nose 20 moves forwards as shown in FIG. 3, whereas the screws 23 are pulled into the magazine 22 when the nose 20 retracts as shown by the broken line in FIG. 3. In other words, whenever the screw tightening operating is carried out, the screws 23 move in the magazine 22 because of a pull and a push by the nose 20. This movement causes some difficulty in carrying out the screw tightening operation.
In addition, when the nose 20 stretches to its full length, a big gap is made between an outlet 24 of the magazine 23 and an inlet 25 of the nose 20. As a result, part of the screws arranged in a line stick out of the gap. Especially when the tightening operation is carried out in a state in which the nose 20 is directed downwards, the chained screws 23 fall out of the magazine 22 and hang down from the gap. This interferes with the operation.